1. Field of the Invention
The present invention relates to a composite optical fiber, an imaging catheter, and a method for producing the same.
2. Description of the Prior Art
An endoscope (hereinafter referred to as an "imaging catheter") is conventionally used to examine blood vessels, the heart, and the interior of body cavities. A typical imaging catheter is shown in FIG. 1 wherein an illuminating light 4 from a light source 1 is guided through an optical transmission fiber 2 into a blood vessel 3. The image of the target, which is formed by a lens installed at the tip of the catheter, is sent back through an image fiber 5 to a direct-vision adapter 6 which enlarges the image for direct viewing by an operator. If the target is the wall of the blood vessel, and its viewing is obstructed by the blood flowing between the catheter and the target, a physiological saline solution 8 is supplied from a syringe 7 and squirted from the top of the catheter to flush away the blood.
As shown in FIG. 2, a composite optical fiber 9, which makes up the imaging catheter that achieves these functions, comprises the image fiber 5, a brine transferring tube 10 and a plurality of small diameter optical fibers 2' for transmitting the illuminating light, and all of these elements are confined in a casing 11 such as a heat-shrinkable tube. However, since the optical fibers 2' are circular in cross section, a gap exists between them and also between the image fiber 5 and the brine transfer tube 10. As a result, the cross-sectional area, through which the illuminating light is transmitted, is relatively small with respect to the overall cross section of the imaging catheter. Furthermore, the casing or sheath 11 that is used to retain the optical fibers 2' around the image fiber 5 unavoidably adds to the outside diameter of the optical fiber 9. As a further disadvantage, assembling and arranging a plurality of optical illumination transfer fibers 2', an image fiber 5 and a brine transfer tube 10 requires considerable time and labor, and, consequently, the cost of producing the composite optical fiber 9 is increased.